Band-gap reference voltage generator

Abstract

A band-gap reference voltage generator comprises an operational amplifier comprising a first input and a second input, the first input being coupled to a first feedback network and the second input being coupled to a second feedback network both coupled to an output of the operational amplifier providing a reference voltage. The first feedback network contains an emitter-base junction of first bipolar junction transistor and the second feedback network contains an emitter-base junction of second bipolar junction transistor. A selectively activated current supply supplies a bias current to the operational amplifier, the current supply being deactivatable in a substantially zero power consumption operating condition for turning the reference voltage generator off. A start-up circuit activated upon start-up of the reference voltage generator for a fixed, prescribed time interval forces a start-up current to flow through the first bipolar junction transistor means.

What is claimed is: 
     
       1. A band-gap voltage reference generator, comprising: an operational amplifier having first and second inputs and an output;   a first resistive feedback network coupled between the output and the first input;   a second resistive feedback network coupled between the output and the second input;   a first diode-configured semiconductor element coupled between the first input and a circuit reference;   a second diode-configured semiconductor element coupled between the second input and the circuit reference;   a current generator coupled to the operational amplifier to supply the operational amplifier with electrical current for operation, the current generator including an enable input terminal to selectively activate the current generator wherein the operational amplifier operates in a normal operational mode when the enable input terminal is selectively activated and, when the enable terminal is not activated, the operational amplifier is non-operational and consumes no power; and   a start-up circuit, electrically coupled to the first diode-configured semiconductor element, to provide a start-up current to the first diode-configured semiconductor element for a predetermined period of time after the enable input terminal is selectively activated.   
     
     
       2. The voltage generator of claim 1 wherein the start-up circuit comprises a semiconductor voltage divider coupled between a power supply voltage and the circuit reference, the voltage divider generating a pre-charge voltage intermediate between the supply voltage and the circuit reference, the pre-charge voltage being applied to the first diode-configured semiconductor element for the predetermined period of time after the enable input terminal is selectively activated. 
     
     
       3. The voltage generator of claim 2, further including an activation circuit coupled to the enable input terminal and the semiconductor voltage divider to activate the voltage divider for the predetermined period of time after the enable input terminal is selectively activated and to deactivate the activation circuit after the predetermined period of time. 
     
     
       4. The voltage generator of claim 3 wherein the activation circuit comprises a digital logic delay circuit coupled to the enable input terminal to generate a first logic level for the predetermined period of time after the enable input terminal is selectively activated and to generate a second logic level after the predetermined period of time. 
     
     
       5. The voltage generator of claim 4 wherein the digital logic delay circuit includes an even number of logic inverters coupled in series to generate a delay time corresponding to the predetermined period of time. 
     
     
       6. The voltage generator of claim 1 wherein the operational amplifier comprises first and second input branches coupled to the first and second inputs, respectively, the first and second branches comprising a plurality of transistors connected in a current mirror configuration. 
     
     
       7. The voltage generator of claim 6, further including a transistor coupled between the first and second input branches to unbalance the first and second input branches for the predetermined period of time after the enable input terminal is selectively activated. 
     
     
       8. The voltage generator of claim 1, further including a transistor coupled between the first and second inputs, the transistor being activated for the predetermined period of time after the enable input terminal is selectively activated to equalize potentials at the first and second inputs. 
     
     
       9. A band-gap reference voltage generator comprising: an operational amplifier having a first input and a second input, the first input being coupled to a first feedback network and the second input being coupled to a second feedback network, both feedback networks being coupled to an output of the operational amplifier providing a reference voltage;   an emitter-base junction of a first bipolar junction transistor within the first feedback network;   an emitter-base junction of a second bipolar junction transistor within the second feedback network;   current supplying means for supplying a bias current to the operational amplifier, the current supplying means being deactivatable in a substantially zero power consumption operating condition for turning the reference voltage generator off; and   start-up circuit means, activated upon start-up of the reference voltage generator for a fixed, prescribed time interval, for forcing a start-up current to flow through the first bipolar junction transistor.   
     
     
       10. The band-gap reference voltage generator of claim 9 wherein the start-up circuit comprises a voltage divider for generating a pre-charge voltage intermediate between a supply voltage and ground, the pre-charge voltage being applied to the emitter-base junction of the first bipolar junction transistor. 
     
     
       11. The band-gap reference voltage generator of claim 10, further including circuit means for activating the voltage divider upon start-up of the reference voltage generator and for deactivating the voltage divider after a prescribed time interval. 
     
     
       12. The band-gap reference voltage generator of claim 10, further including equalizing means activated during said prescribed time interval for equalizing potentials of said first and second inputs of the operational amplifier. 
     
     
       13. The band-gap reference voltage generator of claim 10 wherein the operational amplifier comprises first and second input circuit branches connected in current-mirror configuration, the band-gap reference voltage generator further including unbalancing means activated during said prescribed time interval for unbalancing the first and second input circuit branches of the operational amplifier. 
     
     
       14. The band-gap reference voltage generator of claim 10, further including a bias voltage generator generating at least a first bias voltage for the current supplying means and comprising first means for turning the bias voltage generator off in the substantially zero power consumption operating mode. 
     
     
       15. The band-gap reference voltage generator of claim 14, further including a current-mirror circuit in the bias voltage generator and second means activated in the prescribed time interval for determining an extra current flow through branches of the current mirror circuit.